1. Field of the Invention
This invention relates generally to a heat source providing a substantially constant temperature and more specifically to chemical means providing a source of heat at a temperature which can be controlled to any desired value with particular limits. The invention is particularly adapted to be used in portable baby transporting apparatus.
2. Description of the Prior Art
It is often desirable to provide a portable heat source which can be actuated in a timely manner to provide a substantially constant temperature for an extended period of time. It is even more desirable if such a heat source can be recycled to repeatedly provide a source of heat. Attempts to provide such a heat source are characterized by hot packs, such as those disclosed in copending application Ser. No. 809,870, filed on Mar. 24, 1969, now abandoned, and assigned of record to the assignee of record of the present application. These hot packs include an outer bag for enclosing a first chemical and an inner bag having a rupturable seal and enclosing a second chemical. Upon striking the outer bag, the rupturable seal of the inner bag permits the mixing of the first and second chemicals. These chemicals have had characteristics for reacting to produce a third chemical in an exothermic reaction. Thus, by striking the hot pack, it has immediately provided a source of heat. However, the temperature of the heat has not been particularly constant, nor has the heat been sustained for an extended period of time. Furthermore, these hot packs of the prior art have not been recyclable to repeatedly provide a source of constant temperature heat.
It has been known that many chemicals give off a latent heat of fusion at the substantially constant temperature of their melting point when the chemicals are cooled from a fluid to a solid state. Such a chemical can be heated to a temperature above its melting point to achieve a fluid state. Then when the chemical is placed in an environment having a temperature below its melting point, it would give off its latent heat of fusion at the substantially constant temperature of its melting point. Unfortunately, a heat source incorporating a chemical of this type would not be immediately available for use as the chemical would first have to be heated to achieve a fluid state. If the chemical was additionally heated after it had achieved its fluid state, its temperature would rise so that at least initially the temperature of the chemical would not be constant. Furthermore, since an external source of heat would be needed to initially heat the chemical, it could only be used in proximity to that heat source.
Baby transporting apparatus of the prior art have included an enclosure for the baby in a plurality of electrically energized coils disposed interiorly of the enclosure to provide a source of heat. It is well known that the use of electricity for heating demands a significant magnitude and quantity of electrical energy. This has been particularly objectionable in the baby transporting apparatus of the prior art wherein batteries of significant size and weight have been used to energize the coils. These batteries, which have increased the weight of the prior art apparatus to a magnitude such as 225 Ipounds, have significantly reduced the portability of these apparatus.
The batteries have also been undesirable due to the explosive nature of the gases used as operating aids and anesthetics. As a result of these explosive gases, the baby transporting apparatus of the prior art have been excluded from many areas, such as delivery rooms, wherein their use could be particularly beneficial.
Heat sources such as energized coils have not provided a particularly constant temperature. When the coils have been energized they have been very hot and when they have been de-energized, they have been cold. Therefore, a thermostat has typically been disposed in the environment to be heated for controlling the energizing of the coils in accordance with the temperature of the environment. Thus, the temperature has fluctuated significantly about a desired temperature. Since the coils have achieved extreme temperatures when energized, they have not been placed in contact with the human body, nor have they been coated with a material having a high emissivity to increase the transfer of heat by radiation. Radiant heat is sometimes desirable since it tends to directly heat interior regions of an object, not merely the surface of the object.